Dear friend,
I am an agronomist specialized in soils. I am currently based in Burundi/Rwanda working on the integration waste management with agriculture. The last five years were spent working with the Baha'i Gardens in Haifa (now part of the Unesco World Heritage) investigating on ways to reduce chemical fertilizers and pesticides use in the Garden.

For revitalization of biological processes in the soil, improvement of soil structure, achieving a balanced nutritional status in the soil, and fostering disease suppressiveness, we experimented with different ways of making compost / managing biowastes (i.e., aerobic vs. anaerobic/bokashi; fermentation of food waste with EM followed by aerobic composting then vermicomposting; incorporation of rock dust and/or biochar and/or gypsum).

This background in composting and soil amendments, has shaped my perspective on humanure. I haven't yet seen scientific works comparing dried human excreta to composted human excreta (please share if you are aware of any). However, similar work comparing aged [cow/chicken/pig/horse] manure to composted [cow/chicken/pig/horse] manure exists.
I am aware of some attempts in certain circles to treat humane fecal material by a combination of lactic fermentation (in combination with biochar and rock dust), composting and vermicomposting. This would be similar to what we experimented with on food waste, back in Haifa.

Based on my current understanding, I would think that composting of humanure would yield a better soil amendment than dried humanure, as this tends to be the case for animal manure (that is, if water and nutrient retention, soil structure stability, and disease suppression are factored in).
However, the more elaborate/complex a procedure becomes, the harder and more expensive it becomes for private entrepreneurs or local farmers. Then the question is how to join efficacy of treatment/transformation with simplicity of design?

Dearest friends, I am really sharing these thoughts in a spirit of learning and humility, trying to bring you in our conversation as we try to design the most sustainable management scheme for human excreta in Bujumbura (Burundi)/Kigali (Rwanda). The more bright minds and experience we manage to put together, the better.

Science Journalist - but rarely about sanitation.. all views and errors mine

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Dear Dr Guillaume Nyagatare,

Can I just be clear what you are asking for - do you want to see benefits to the soil of dried vs composted human faeces? Or do you mean in terms of the destruction of pathogenic microbes in the faeces?

Previously trained and worked as a Soil Scientist and worked on projects composting sewage sludge.

I am a backyard tinkerer (trained as a biologist). I have lived in Zimbabwe for 42 years, where I have worked, amongst other things, on rural water supply and sanitation.

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Dear Guillaume,

I have seen your question on the Susana website a few weeks ago concerning comparisons made between dried and composted human “manure.” It is possible that you already have received answers from our learned colleagues at the Universities, such as the agricultural college in Uppsala, Sweden, who have the equipment to test for such things.
We have done some rather simple work here in Zimbabwe on the nutrient levels in composted human waste. I attach some of the findings.

These have been mainly concentrating on human compost processed in the Fossa alterna, where both urine and faeces are added to shallow composting pits together with soil, wood ash and very often leaves as well.

In urine diverting toilets that I have used myself, soil and ash are added as well, and in the single chamber version that I studied, where the faeces fell into buckets, this mix of faeces, soil, ash and toilet paper were moved from the buckets into separate composting chambers where more soil and leaves were added.

Where the human faeces (in urine diversion) or combination of faeces and urine (in Fossa alterna) build up together with soil, and ash and hopefully leaves as well (representing plant matter), the resulting nutrient content is likely to be rather different from dried faeces alone.

We did undertake testing of the “compost” produced from the Fossa alterna. And also performed plant trials. These have been documented in work entitled “An ecological approach to Sanitation” which was posted in 2006 (SEI Stockholm). I shall have to look closely to see if tests were also made in the compost produced from the urine diverting toilet (where soil, ash and leaves were added).

I think the bottom line is that where the faeces just dry out with a drying or bulking agent like ash (which I think is the norm for most urine diverting toilets) the nutrient content will have useful amounts of phosphorus and potash but not much else, as the nitrogen will have been lost. However if the faeces or combination of faeces and urine are mixed with soil, ash and leaves, a better balance of nutrients will result with a much more suitable (crumbly) texture for use in agriculture.

I think the tests and results of these early works is on the Susana website. See the individual chapters attached below.
Hope this helps

Best wishes

Peter Morgan
Zimbabwe

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This is an interesting topic indeed, although I think that in most cases the simplicity of just drying the feces outweighs the potential advantages of a proper compost as soil conditioner.

Besides the NPK nutrients one has probably have to look at the specific humic substances that are created in the warm and micro-aerobic interior of a compost heap. They are probably what gives the most benefit as a soil conditioner.

Thank you so much for you thorough reply. Unfortunately, Internet connectivity can be occasionally frustrating from our end. I read the documents that you kindly attached. I noticed that the method that you use for composting avoid contact with fresh humanure - which is a commendable thing. There no need to turn, as it is usually done with compost.

It seems to me that given the size of the composting pits (less than 1 m3), and the amount of soil added (50% V/V) heat will not be generated. We are thus dealing with a mesophilic composting, relying mostly on biological processes and time for the elimination of pathogens.

I noticed with great interest that the nature of the container used during composting influences the nutrients remaining at the end of composting. What explanation did you come up with for the differences noted among containers types?

Assuming that the same material was used for those trials, would it not be reasonable to hold that the differences in nutrients contents could be due to differences in aeration and drainage? If this is the case, then N, and to a lesser extent, K, would be affected. However in your papers, P was also affected.

Greater aeration could result in greater loss of N (mirroring C losses), whereas greater drainage in combination with excessive watering would result in greater N and K (both in soluble (as ions) and particulate (organic) forms). P should then be lost mostly in organic particulate form during excessive leaching events associated with excessing watering.

This is to say that with different types of containers, we are in fact having different aeration and drainage conditions?

In your experiment with rape, urine seemed to have been detrimental to plant growth. It would be interesting to see whether the combination of urine with compost tea would "neutralize" the toxic effect of urine on sensitive plants. In my experience, compost tea alone can help keep the plant vigorous during times of stress.

I am a backyard tinkerer (trained as a biologist). I have lived in Zimbabwe for 42 years, where I have worked, amongst other things, on rural water supply and sanitation.

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Thank you Guillaume for your response,

Indeed the process which takes place in the pits is mesophilic which relies on biological processes and time and not the generation of heat. The volume of the pit varies somewhat being smallest in the Arborloo and larger in the Fossa alterna, and larger still in the so called long cycle Fossa alterna, which is still on trial.

You said:

I noticed with great interest that the nature of the container used during composting influences the nutrients remaining at the end of composting. What explanation did you come up with for the differences noted among containers types?

In the various experiments, the mix of excreta and soil and ash added to urine diverting toilets in the so called “skyloo” an elevated urine diverting toilet with a single vault and where the materials enter a bucket, which is them emptied in a variety of composting sites or containers. Early experiments used composting jars, then alternating composting pits. Extra ingredients were added to these composting sites, notably leaves and more soil. In each case the material turned into a crumbly pleasant soil much like compost. With the Arborloo, the conversions take place under ground and out of site. The roots of the young tree planted at first penetrate the soil which is added on top of the excreta/soil mix beneath. Then the roots will penetrate further when the plant (tree) itself assesses the nature of the composted material.

In the case of the material extracted from the Fossa alterna, there are various destinations. The material can be placed in the lower half of so called “tree pits.” Here the upper half if the pit is topped up with topsoil and the tree planted. Alternatively the topsoil of a vegetable bed can be removed and the material from the Fossa alterna spread over the excavation. Then the topsoil is replaced. The two layers can be mixed.

You said:

Assuming that the same material was used for those trials, would it not be reasonable to hold that the differences in nutrients contents could be due to differences in aeration and drainage? If this is the case, then N, and to a lesser extent, K, would be affected. However in your papers, P was also affected.

The material used originates from a number of different toilets and times of year. Therefore there would be differences in temperature. Also the precise amount of soil and sash and even leaves added varied in the different toilets. The nutrient level of the soil added would also vary. The quality and nutrient level of the final product would vary depending on the type of soil, and the amounts of additional materials added. Also, particularly in countries with people who suffer from inadequate diets, there will be a variation in the amounts of nutrients held in the excreta. Perhaps since you are a professional in this field, you can provide an answer to your own question.

You said:

Greater aeration could result in greater loss of N (mirroring C losses), whereas greater drainage in combination with excessive watering would result in greater N and K (both in soluble (as ions) and particulate (organic) forms). P should then be lost mostly in organic particulate form during excessive leaching events associated with excessing watering.

Well the points you make are valid and interesting. There is a lot of variation between toilets and also the users. The soil type, related to drainage, varies enormously. I have tried to keep things simple. Perhaps you should take up the challenge and try to answer your own questions.

You said:

This is to say that with different types of containers, we are in fact having different aeration and drainage conditions?

I am sure there is great variation depending on container type.

You said:

In your experiment with rape, urine seemed to have been detrimental to plant growth. It would be interesting to see whether the combination of urine with compost tea would "neutralize" the toxic effect of urine on sensitive plants. In my experience, compost tea alone can help keep the plant vigorous during times of stress.

In my experiments the application of dilute urine increased the growth and production of rape as well as other green vegetables. I am sure compost tea, or just simply good compost, whether it came via the toilet route or through the garden compost heap, would also invigorate plant growth.

Overall the best food for plants comes from natural well-made compost and added to topsoil. Too much urine, if improperly added can indeed kill off some less tolerant plants, and also add excess salts to the soil, if the same patch of soil is used repeatedly.

I would urge you to continue with your own experiments and report to this forum.